there is a workaround to get what you want by using the dual function.
Seems you have a line chart and marked 'Values on Datapoints' on the expression tab. Call this expression 'expression1'.
In order to get your desired result add a new expression like this: expression2 = Dual(Num(expression1, '# ##0.0'), expression1 + const.) , check 'Values on Datapoints' for this second expression and also 'Invisible'. Now uncheck 'Values on Datapoints' for your first expression. Very important thing is to go to the number tab and mark the 'Expression Default' checkbox for expression2 otherwise the dual function does not work.
The term const. is just the amount you want to shift the 'Values on Datapoints' up or down . If you want you can use a variable vShift instead of conts. and use a slider to adjust the shift easily.